At my last session at Lake George I had a Close Shave with my SA Speeed Demons team mate Choco. As you can see from the footage I thought I was aware of all the sailors in my vicinity! I started off a few hundread meters from another sailor and followed. I passed them over the top and scanned back and forth for other sailors. You can see a slight haze in my luff pocket at 1:43 and then Choco appears. The nose of his board clipped the foot of my sail and if I had been a second later who knows what might have happened. There was no reason to stop and I was on a NM so I finished the run and caught up with Choco later.
I have never had such a close shave and I think the conditions were a contributor. You could sail fast on all tacks at a constant speed so 2 sailors could converge on a point from a long distance away being blissfully unaware of each other. Choco was hidden by my luff pocket and I was in his blind spot upwind.